The temperature of a human or animal, can be measured either by means of thermal conduction or thermal radiation. In the former case, a temperature sensing probe may be positioned inside the patient's body cavity or on the skin surface to obtain an intimate contact for conductively receiving thermal energy indicative of a surface temperature of a patient-measured body site. In the latter case, a naturally-emanated electromagnetic radiation in the mid- and far-infrared spectral ranges may be detected by an appropriate non-contact sensor, whose output signal is indicative of the surface temperature of a patient-measured body site (for example, in proximity to the tympanic membrane). A combination of a sensor, electronic circuit and other components form an infrared (IR) thermometer, which is an opto-electronic instrument.
Many medical thermometers, either contact or non-contact, use sanitary probe covers which envelope the probe and prevent cross-contamination of patients and soiling of the probe. In a contact probe cover, thermal energy (heat) is transmitted by means of thermal conduction. Thus, requirements for the probe cover must be compatible with the thermally conductive properties of the probe cover material. Various conventional covers for such contact thermometers are described in many patents, for example, in U.S. Pat. No. 4,159,766 to Kluge, which is incorporated by reference herein in its entirety.
In order to measure a surface temperature of an object by means of IR radiation, the probe of the IR thermometer is aimed at the area of interest. For example, in order to measure the temperature of a tympanic membrane and the surrounding tissues, the probe is placed into the ear canal. Before the insertion, a probe cover is typically installed onto the probe to envelope its parts that otherwise might come in contact with the tissues of the ear canal.
A typical prior art infrared thermometer 70 is illustrated in FIGS. 1a and 1b. The thermometer 70 includes a front end 77, from which an infrared probe 72 projects, for example, with an orientation suitable for placement of the probe 72 in the ear canal. A probe cover 71 is positioned to be placed over the probe 72 for eliminating any direct contact between the probe 72 and tissues of the ear canal. A power button 76 is provided for powering the circuitry of the thermometer 70. A start button 78 is provided to engage the circuitry to perform a temperature measurement, and a display 75 is provided, for example, to indicate a current condition or status of the thermometer 70 and/or the results of a current temperature measurement. A probe cover detector 73 is positioned near a base of the probe 72 for detecting that the probe cover 71 has been placed over the probe 72, and may for example interact with the circuitry to permit operation of the thermometer 70 only when installation of the probe cover 71 has been detected. After a temperature measurement has been made, a probe cover ejector 74 elevates the front end 77 of the thermometer 70 relative to the probe 72 in order to eject the probe cover 71 from the probe 72.
The probe cover 71 is not only required to provide a sanitary protection against contamination of the probe by ear wax and other soiling biological compounds, but it must possess other properties for accurate temperature measurement by means of detecting an associated IR signal. Such properties, for example, include a good optical transparency of the probe cover in the spectral range of interest, low directional distortion of optical rays, tight manufacturing tolerances, stability of the optical properties during installation onto the probe, long term stability, and the like. Suitable probe covers for IR thermometers are exemplified by U.S. Pat. No. 5,088,834 issued to Howe et al. and U.S. Pat. No. 5,163,418 issued to Fraden et al., each of which is incorporated by reference herein in its entirety. Most prior art probe covers are formed to surround a longitudinal axis of a thermometer probe.
As a rule, a prior art probe cover intended for a medical thermometer includes three portions being disposed along the probe longitudinal axis y (see, e.g., FIG. 2a):
1) a proximal or “base” portion 102 provided for physical retention of the cover by the thermometer probe or front end of a thermometer housing. The proximal portion 102 may contain an offset 3 for interaction with the retention devices of the probe. This offset 3 is disposed along a transverse axis x that is substantially normal to longitudinal axis y. A brim 7 may or may not be part of the proximal portion 102. The proximal portion 102 has an opening 105 through which the probe is inserted during a probe cover installation. Instead of or in addition to the offset 3, the proximal portion 102 may have a snug fit over the probe, thus using friction as a retention force (see, e.g., FIG. 2e),
2) a middle or “body” portion 101 provided for enveloping the sides of the probe. The middle portion 101 includes a rigid or pliant wall 1. The middle portion 101 may be prefabricated, or it may be formed during the probe cover installation by stretching wall 1 to match the probe length, and
3) a distal or “tip” portion 100 provided for enveloping the optical end of the probe of an IR thermometer or the sensing part of a contact thermometer. This portion 100 contains a membrane 2 which is substantially transparent for IR radiation (for an IR thermometer), or is thermally conductive (for a contact thermometer). The membrane 2 may include a polymer film (for an IR thermometer, in thickness ranges from as little as 0.0005 in. to as much as 0.005 in.). The IR radiation passes through the membrane 2 before entering the probe where it is detected by the IR sensor. In effect, the membrane 2 of the probe cover works as an optical filter, and often is alternatively called a “lens filter.”
Typical materials for fabricating the probe covers are polyethylene, polypropylene, and copolymers of polyethylene and polypropylene. FIG. 2a shows a prior art unitary probe cover (as taught for example by U.S. Pat. No. 5,088,834) which is fabricated as a single piece. FIG. 2b shows a two-piece probe cover (as taught by U.S. Pat. Nos. 4,662,360, 5,293,862 and 5,179,936, each issued to O'Hara et al. and incorporated by reference herein in their entirety) where a membrane 6 is welded onto a frustoconical body 4. In the probe cover of FIG. 2b, a bottom ring 5 is provided for affixing the probe cover to the probe as part of a proximal portion. Probe covers generally have shapes that follow a body of rotation around a longitudinal axis y.
Probe covers may be attached to the probe or the IR thermometer housing by various mechanisms. FIG. 2c once again shows the offset 3, which is an extension of wall 1 of the probe cover in the proximal portion 102. The offset 3 engages a nipple 12 that is part of a probe 8 of the IR thermometer when the probe cover is installed onto the probe 8. The nipple 12 is disposed along a transverse axis x.
Another known way of attaching a probe cover to a probe is shown in FIG. 2d. FIG. 2d illustrates a hook 10 (also illustrated in FIG. 2b) which is supported by a neck 11. The neck 11 is an extension of a ring 5. When the probe cover is installed onto the probe 9, hook 10 engages a retention skirt 49 of a probe cover 9. The retention portion 40 of hook 10 is disposed along the transverse axis x. Alternatively, FIG. 2e shows a probe cover 4 installed on a probe 9, which includes a retention ring 5 that enables the probe cover 4 to be retained by a frictional force applied to the probe cover 4 along the transverse axis x.
In the prior art probe covers illustrated in FIGS. 2a-2e, a probe cover body is formed along the longitudinal axis y, having retention elements formed along the transverse axis x.
Known prior probe covers, while having various shapes and methods of retention, often may be interchanged between different types of thermometers. This is undesirable, and may for example cause a mismatch between the type of a membrane 2 (material, thickness and shape) and the thermometer calibration and, as a result, cause unacceptably high errors in temperature measurement. It is important to use only a correct (matching) probe cover with a particular thermometer. However, common matching techniques such as affixing an identification code on a probe cover are typically insufficient for preventing use of a wrong probe cover. Thus, a more direct method for preventing usage of a foreign probe cover on a thermometer is desirable.